As mobile device technology continues to develop and demand therefor continues to increase, demand or secondary batteries as energy sources is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which have high energy density and operating voltage, long cycle lifespan, and low self-discharge rate, are commercially available and widely used.
In addition, as interest in environmental problems is recently increasing, research into electric vehicles (EVs), hybrid EVs (HEVs), and the like, that can replace vehicles using fossil fuels, such as gasoline vehicles, diesel vehicles, and the like, which are one of the main causes of air pollution, is actively underway. As a power source of EVs. HEVs, and the like, a nickel metal-hydride secondary battery is mainly used. However, research into lithium secondary batteries having high energy density, discharge voltage and output stability is actively underway and some lithium secondary batteries are commercially available.
A lithium secondary battery has a structure in which an electrode assembly, in which a porous separator is interposed between a cathode and an anode, each of which includes an active material coated on an electrode current collector, is impregnated with a lithium salt-containing, non-aqueous electrolyte.
Anodes of conventional lithium secondary batteries mainly use, as an anode active material, carbon-based compounds that maintain structural and electrical properties and enable reversible intercalation and deintercalation of lithium ions. However, recently, research into anode materials prepared by alloying Li with silicon (Si) or tin (Sn) and lithium titanium oxides (LTO) instead of conventional carbon-based anode materials has been underway.
Lithium titanium oxides (LTO) are materials that hardly undergo structural changes during charging and discharging and thus exhibit zero strain. In addition, lithium titanium oxides are known to have excellent lifespan characteristics, have a relatively high voltage range, and not to form dendrites, thus exhibiting excellent safety and stability. In addition, lithium titanium oxides (LTO) have electrode characteristics such as quick charging and thus may be charged in several minutes.
However, since lithium titanium oxides (LTO) absorb moisture in the air, when an electrode is manufactured using the lithium titanium oxides (LTO), moisture is scattered and generates a great quantity of gas. The generated gas may cause deterioration of battery performance.
Thus, when lithium titanium oxides as anode active materials are used in lithium secondary batteries, a drying process at a high temperature is required for removal of moisture. However, porous polyolefin based films conventionally used as a separator in lithium secondary batteries shrink at high temperature and as such, cause problems such as an internal short circuit and the like.
Therefore, there is an urgent need to develop technology for a material which is stable at high temperature to remove moisture.